Moving forward…slowly

A combination of Christmas preparation, overtime and water leakage took most of the time during the last week so not much progress was done

So what’s the current status in the project? Well, we are still discussing with Seeedstudio on how to start up but most of the things are now in place. We are continuously working on the software/firmware and wiki when we have spare time. Also since we don’t really know how many kits we will sell we are aiming at having a two week pre-order phase before the production of the kits begin.

I’m planning on developping some kind of area mapping hack for your quadrotor. The idea is to use a ranging sensor, considering ultrasound, and knowing xyz+pitch,yaw,roll we can then know the relative altitude of a ranged point in space. Of course it could also be used to stabilize altitude.

I need to design a frame to attach the sensor to. I’m planning to use the 4 (I read somewhere their diameter is about 0.9mm is that correct ?) holes on the corners of the PCB to attach the frame. Therefore I’d like to know if you could provide a CAD model of the PCB frame or just communicate the xy position and diameter of the holes.

Would be greatly appreciated so I can already laser cut a frame for the sensor and start testing.

Great idea. We have been thinking about ultrasound sensors as well but most of them are a bit big and heavy. Have you found a small an light one? Are your idea to use the three ultrasound sensors to get the xyz coordinates? Just trying to figure out if your idea is possible to realize.

The mounting holes are ~0.9mm in diameter, actually plated 1 mm holes. they are formed as a cube, 34mm center to center.

The idea is we already know the XYZ and pitch roll yaw of the platform via the onboard accelerometer and gyro. (maybe the optional baro and magnetometer may get usefull but i’m worried about the motors magnetic noise..).

So knowing the relative position and angles of the platform in space, we could now mount a unique ultrasound sensor (like this one, accurate to 1mm, 10hz reading, rs232 or ttl, ranging from 300 to 5000mm http://www.maxbotix.com/Ultrasonic_Sensors.htm#HRLV-EZ). The idea is to position the sensor in the middle under the quadcopter. so it gives a reading vertically perpendicularly to the platform. Then knowing XYZ, the angles and the distance to an object where the belly of the platform is pointing we can draw te elevation of the apparent ground relative to the height of the quadcopter.

Here is some 3D render of the current state with 50mm spacing and 0.9 holes. Mount is made out of PMMA with 1mm arms (not sure if they are strong enough though, I’ll try out different sizes). Total weight is about 4.7 grams without the cables. We need 4 cables for RX TX VCC and GND and maybe a cap to filter the battery voltage if it fluctuates a lot. That weight looks reasonable regarding payload capabilities.

As for the weight of 4.7 grams it should be fine but I have some concerns though.

– It looks like the sensors runs of 5V but maybe it is possible to run on other voltages as well. The voltages on the Crazyflie are set with adjustable regulators so it is possible to change them from the 2.8V they are configured at now. Actually setting the digital VCC to 3.3V is as simple as grounding a soldering point.

– Getting the XYZ might be the big problem. We have not tested anything such as that and my experience says that the measurements from the accelerometer is to noisy (from vibrations) to get any usable readings to compute the XYZ.

It runs on anything from 2.5V to 5.5V. Range and beam characteristics get affected by the voltage, but max range would still be around 4850 mm so reasonable in an indoor context. So 2.8 should be just fine.

Concerning XYZ: the platform looked very stable in the air and therefore I thought it had a good knowledge of it’s current XYZ speeds (hence positions). Maybe I concluded a bit quickly on that part.

This elevation mapping project is more of a challenge anyway, the idea is to quickly scan a surface of maybe 4 m^2 or so with a resolution of about 10 cm^2 that makes about 400 mesures to take at a rate of 1 Hz it’s a bit over 6 minutes but it seems manageable.

If there is no way to get a good XYZ with the gyro/accelerometer it’ll only serve as altitude hold for the moment. Maybe some floor facing camera following lines on the ground could do it, but that would require programation skills a bit over my head for now. Multiple ultrasound sensors could work too, but that would be heavy.

The other option of course would be to spot the platform from ground mounted cameras for XY and use an add-on baro for Z. But that’s getting complicated. The idea is to have an integrated solution which sounds feasable.